Both zones are over the islands known as Diaoyu in China and Senkaku in Japan.
The islands, known as Senkaku in Japanese or Diaoyu in Chinese, are also claimed by Taiwan.
Long curved chains of islands known as island arcs form at such subduction zones.
A magnificent seascape is dominated by Ramsey Island and the line of islands known as the Bishops and Clerks.
The East China Sea islands, known as the Diaoyu in China, are administered by Tokyo but claimed by Beijing.
The picturesque islands, known as Norway in miniature, are famous for their wildlife, including whales, seals, moose and eagles.
Most of the rest were shipped to the Caribbean, to islands known, at the time, as graveyards.
Tensions with Japan over the Senkaku islands (known in China as the Diaoyu) have been mounting again.
The Chinese government on Monday was largely silent about the islands, known as the Senkaku in Japan.
(Japan is also in a dispute with South Korea over the Takeshima islands, known in Korea as the Dokdo islands).
The islands, known internationally as the Paracels but in Chinese as the Xisha, are claimed by China, Vietnam and Taiwan.
